The present invention relates to a piezoelectric/electrostrictive device having a movable portion to be operated based on a displacement of a piezoelectric/electrostrictive element, or a piezoelectric/electrostrictive device capable of detecting a displacement of the movable portion by the piezoelectric/electrostrictive element, and more particularly relates to a piezoelectric/electrostrictive device which is superior in mechanical strength, impact resistance, and humidity resistance and can efficiently operate the movable portion in a large magnitude.
Recently, in a field of optics or magnetic recording, precision machining, or the like, a displacement element capable of adjusting an optical path length and a position in sub-micron order has been required, and development has progressed of a displacement element utilizing a displacement due to the inverse piezoelectric effect or electrostrictive effect obtained when a voltage is applied to a piezoelectric/electrostrictive material (for example, a ferroelectric substance or the like). For example, as shown in FIG. 2, a piezoelectric actuator 21 in which a fixing portion 25 and a movable portion 24 and a bridge beam 26 connecting therewith are integrally formed by providing a hole 28 on a board-like body composed of a piezoelectric/electrostrictive material, and an electrode layer 22 is further provided on the bridge beam 26, is disclosed in JP-A-10-136665.
In the actuator 21, when a voltage is applied to an electrode layer 22, the movable portion 24 can have an arc-shaped displacement or a rotational displacement in the plane of the board-like body, since the bridge beam 26 expands or contracts by the inverse piezoelectric effect or electrostrictive effect in a direction connecting the fixing portion 25 with the movable portion 24.
On the other hand, JP-A-63-64640 discloses a technique related to an actuator using a bimorph, wherein the bimorph is provided with divided electrodes such that a divided electrode is selected to drive the actuator to perform precise alignment at a high speed. For example, the specification shows in FIG. 4 a structure which uses two bimorphs positioned opposing to each other.
However, the actuator 21 has a problem that an operational quantity of the movable portion 24 is small, since the displacement in an expanding or contracting direction (namely, the in-plane direction of the board-like body) of a piezoelectric/electrostrictive material is transmitted per se to the movable portion.
Further, the actuator 21 has another problem that the actuator 21, having all the parts thereof constituted with a piezoelectric/electrostrictive material which is fragile and comparatively heavy, is low in mechanical strength, and inferior in handling property, impact resistance and humidity resistance, and further the actuator 21 per se is heavy and is easily influenced by a harmful vibration, for example, residual vibration or vibrational noise during high speed operation.
In order to solve above-described problems of the actuator 21, a proposition is made that a hole 28 is filled with an elastic filler. However, it is apparent that efficiency of the displacement due to the inverse piezoelectric effect or the electrostrictive effect is lowered when the filler is added.
On the other hand, what is shown in FIG. 4 of JP-A-63-64640 is, in bonding of an intermediary member 3 and a bimorph, a bonding of a site without the divided electrodes with the intermediary member, and therefore an advantage of the divided electrodes cannot be utilized at the bonded site. In other words, merely a site of the bimorph which is not a displacement generating portion is bonded. Further, on the other hand, a bonding formed at a bonding site of a head and the bimorph is similar. As a result, a bending displacement of the bimorph is developed toward an inner space between the intermediary member and the head, and the structure is not a type where the head per se is given an operation for effective displacement toward the outside space. In addition, the actuator disclosed in JP-A-63-64640 has a structure where a displacement generating member and a so-called frame member (an intermediary member or the like) are prepared separately, and adhered mutually to unite, thus the structure is liable to change over time the bonding condition of the frame and the bimorph, and also liable to cause drifting of the displacement, exfoliation, or the like. Further, a structure with an adhesive intervened at the bonding site of the bimorph with the intermediary member and at the bonding site of the head with the bimorph, namely at a holding portion of a displacement member, is lower in stiffness at the holding portion per se, thus making it difficult to increase a resonant frequency required for high speed operation.
The present invention is made in view of such problems in the conventional art, and an object thereof is to provide a displacement element which can largely operate a movable portion, and is hardly influenced by a harmful vibration in operation, capable of a high speed response, high in mechanical strength, and superior in handling property, impact resistance, and humidity resistance, as well as a sensor element capable of detecting a vibration of the movable portion in fine precision, and methods of fabricating the elements.
According to the present invention, firstly provided is a piezoelectric/electrostrictive device comprising a driving portion to be driven by a displacement of a piezoelectric/electrostrictive element, a movable portion to be operated based on a drive of the driving portion, and a fixing portion for holding the driving portion and the movable portion, said piezoelectric/electrostrictive device being characterized in that the driving portion is formed of a pair of thin plate portions facing each other, and a film-like piezoelectric/electrostrictive element including at least a pair of an electrode films and a piezoelectric/electrostrictive film formed on at least a part of the outer surface of at least one thin plate portion of the thin plate portions, the fixing portion is coupled with the movable portion via the driving portion, a hole is defined by an inner wall of the driving portion, an inner wall of the movable portion, and an inner wall of the fixing portion, at least one side of a piezoelectric operating portion of the piezoelectric/electrostrictive element in a direction connecting the fixing portion with the movable portion is structured to exist on the fixing portion or the movable portion, and a ratio a/b of the thickness a of the hole and the width b of the thin plate portion is 0.5 to 20.
Further provided in the present invention are a piezoelectric/electrostrictive device characterized in that the width of the thin plate portion is the same as the width of the piezoelectric/electrostrictive element formed on the thin plate portion; a piezoelectric/electrostrictive device characterized in that a ratio e/a of the length e of the thin plate portion and the thickness a of the hole is 0.5 to 10; a piezoelectric/electrostrictive device characterized in that a ratio a/b of the thickness a of the hole and the width b of the thin plate portion is 1 to 10, and a ratio e/a of the length e of the thin plate portion and the thickness a of the hole is 0.7 to 5; and a piezoelectric/electrostrictive device wherein the movable portion and the fixing portion are a rectangular solid body.
According to the present invention, secondly provided is a piezoelectric/electrostrictive device comprising a driving portion to be driven by a displacement of a piezoelectric/electrostrictive element, a movable portion to be operated based on a drive of the driving portion, and a fixing portion for holding the driving portion and the movable portion, said piezoelectric/electrostrictive device being characterized in that the driving portion is formed of a pair of thin plate portions facing each other and a film-like piezoelectric/electrostrictive element comprising at least a pair of electrode films and a piezoelectric/electrostrictive film formed on at least a part of the outer surface of at least one thin plate portion of the thin plate portions, the fixing portion is coupled with the movable portion via the driving portion, a hole is defined by an inner wall of the driving portion, an inner wall of the movable portion, and an inner wall of the fixing portion, and at least one side of a piezoelectric operating site of the piezoelectric/electrostrictive element in a direction connecting the fixing portion and the movable portion is structured to exist on the fixing portion or the movable portion, the thickness a of the hole is 100 xcexcm to 2000 xcexcm, and the width b of the thin plate portion is 50 xcexcm to 2000 xcexcm.
Further provided are a piezoelectric/electrostrictive device characterized in that the thickness a of the hole is 200 xcexcm to 1000 xcexcm and the width b of the thin plate portion is 100 xcexcm to 500 xcexcm; a piezoelectric/electrostrictive device characterized in that the width b of the thin plate portion is larger than the thickness d thereof, and the thickness d is 2 xcexcm to 100 xcexcm; a piezoelectric/electrostrictive device characterized in that the length e of the thin plate portion is 200 xcexcm to 3000 xcexcm; a piezoelectric/electrostrictive device characterized in that the length f of the movable portion is 50 xcexcm to 2000 xcexcm; a piezoelectric/electrostrictive device wherein said piezoelectric/electrostrictive device has at least two driving portions; a piezoelectric/electrostrictive device wherein said piezoelectric/electrostrictive element is a laminated type piezoelectric/electrostrictive element with a lower electrode film, a piezoelectric/electrostrictive film, and an upper electrode film laminated in a layer form; a piezoelectric/electrostrictive device wherein said piezoelectric/electrostrictive element is structured with a piezoelectric/electrostrictive element comprising a piezoelectric/electrostrictive film and a first electrode film and a second electrode film formed on at least one main surface of the piezoelectric/electrostrictive film; a piezoelectric/electrostrictive device wherein said piezoelectric/electrostrictive element is a piezoelectric/ electrostrictive element having a structure in that a piezoelectric/electrostrictive element comprises a piezoelectric/elecrostrictive film and a first electrode film and a second electrode film of comb-type structure, and the first electrode film and the second electrode film are alternatively biting with a gap of a predetermined width between respective teeth of each comb; a piezoelectric/electrostrictive device in which the movable portion, the thin plate portion, and the fixing portion are an integrally formed ceramics; a piezoelectric/electrostrictive device wherein said ceramics is a laminate of the ceramic; and a piezoelectric/electrostrictive device characterized in that at least one side in a direction connecting the fixing portion with the movable portion of a piezoelectric operating portion in the piezoelectric/electrostrictive element exist on the movable portion or the fixing portion, extending from bonding portion of the movable portion with a thin plate portion or a bonded portion of the fixing portion with a thin plate portion and over at least one half of the distance of the thickness d of the thin plate portion.
Furthermore, thirdly provided in the present invention is a method of fabricating a piezoelectric/electrostrictive device comprising a driving portion to be driven by a displacement of a piezoelectric/electrostrictive element, a movable portion to be operated based on a drive of the driving portion, and a fixing portion for holding the driving portion and the movable portion,
said piezoelectric/electrostrictive device being provided in that the driving portion is formed of a pair of thin plate portions facing each other, and a film-like piezoelectric/electrostrictive element comprising and at least a pair of electrode films and a piezoelectric/electrostrictive film formed on at least a part of the outer surface of at least one thin plate portion of the thin plate portions, the fixing portion is coupled with the movable portion via the driving portion, a hole is defined by an inner wall of the driving portion, an inner wall of the movable portion, and an inner wall of the fixing portion, and at least one side in a direction connecting the fixing portion with the movable portion of a piezoelectric operating portion of the piezoelectric/electrostrictive element is structured to exist on the fixing portion or the movable portion;
said method of fabricating the piezoelectric/electrostrictive device being characterized by including steps of preparing a ceramic green laminate comprising at least one ceramic green sheet to become a thin plate, and at least one ceramic green sheet having at least one hole formed thereon, sintering the ceramic green laminate to produce a ceramic laminate, forming a piezoelectric/electrostrictive element by a film forming method on the outer surface of the thin plate of the ceramic laminate obtained, and cutting the ceramic laminate having the piezoelectric/electrostrictive element formed thereon.
Further provided are a method fabricating a piezoelectric/electrostrictive device wherein the steps of preparing a ceramic green laminate include a step of preparing ceramic green sheets become a pair of thin plates in such manner that they are laminated facing each other; a method fabricating a piezoelectric/electrostrictive device wherein the steps of preparing a ceramic green laminate include a step of preparing ceramic green sheets to become a pair of thin plates in such a manner that they are laminated on the outermost layers facing each other, respectively; a method of fabricating a piezoelectric/electrostrictive device wherein the steps of preparing a ceramic green laminate include a step of preparing a laminate by laminating a ceramic green sheet to become a thin plate with at least one ceramic green sheet having at least one hole formed thereon; a method of fabricating a piezoelectric/electrostrictive device wherein the steps of preparing a ceramic green laminate include a step of preparing a laminate by laminating a ceramic green sheet to become a thin plate with a desired number of the ceramic green sheets having each at least one hole formed thereon; and a method of fabricating a piezoelectric/electrostrictive device wherein the steps of preparing a ceramic green laminate include a step of preparing a laminate by laminating at least one ceramic green sheet having at least one hole formed thereon with ceramic green sheets to become a pair of thin plates in such a manner that ceramic green sheets to become a pair of thin plates are placed by facing each other on the outermost layer of the ceramic green laminate.
Further provided are a method of fabricating a piezoelectric/electrostrictive device wherein the steps of preparing a ceramic green laminate include steps preparing two laminates A by laminating a ceramic green sheet to become a thin plate laminated with at least one ceramic green sheet having at least one hole, respectively, preparing one green sheet having at least one hole formed thereon or a laminate B by laminating a plurality of ceramic green sheets having at least one hole formed thereon, and laminating laminates A by intervening said one ceramic green sheet having at least one hole formed thereon or the laminate B in a such manner that respective thin plate portions are placed at the outermost layer, respectively, when the laminate is prepared; a method of fabricating a piezoelectric/electrostrictive device characterized in that a protrusion is provided on a portion on an outside surface of a layer of at least one side of the outermost layer of the ceramic green laminate excluding at least the thin plate portion; a method fabricating of a piezoelectric/electrostrictive device wherein said method of fabricating a piezoelectric/electrostrictive device includes steps of laminating, on a outermost layer of a laminate comprising ceramic green sheets having at least one hole formed thereon, respectively, a ceramic green sheet having at least one hole formed thereon which is mounted on a plastic film in such a manner that said plastic film becomes a new outer layer when at least a plurality of ceramic green sheets having at least one hole formed thereon, respectively is laminated, and then removing the plastic film after holes are accurately aligned; a method of fabricating a piezoelectric/electrostrictive device, wherein said method of fabricating a piezoelectric/electrostrictive device includes steps of laminating a ceramic green sheet having at least one hole formed thereon which is mounted on a plastic film on a ceramic green sheet to become the thin plate in such manner that the plastic film is placed as an outer layer, and removing the plastic film after holes are accurately aligned; a method of fabricating a piezoelectric/electrostrictive device where the plastic film is a poly(ethyleneterephthalate) film; a method of fabricating a piezoelectric/electrostrictive device, wherein a ceramic laminate with a piezoelectric/electrostrictive element formed on the outer surface of the thin plate portion is further cut into a plurality of desired units, and then the cut units are heat treated at 300xc2x0 C. to 800xc2x0 C.; and a method of fabricating a piezoelectric/electrostrictive device, characterized in that when a ceramic laminate with the piezoelectric/electrostrictive element formed thereon is cut, the piezoelectric/electrostrictive element and the laminate is simultaneously cut so as to make the width of the piezoelectric/electrostrictive element the same as the width of thin plate portion of the laminate.
It is preferable that a piezoelectric/electrostrictive device according to the present invention comprises, as aforementioned, a movable portion, a thin plate portion, and a fixing portion in an integrally formed ceramic, and it is more preferable that the moving portion, the thin plate portion, and the fixing portion are composed of a material with fully-stabilized zirconia as a major component or a material with partially-stabilized zirconia as a major component, and it is specifically preferable that at least a movable portion, a thin plate portion, and a fixing portion are a sintered ceramic green laminate. This is because the bonded portion between a movable portion, a thin plate portion, and a fixing portion can be made a borderless structure by sintering integration, thus long term reliability with lapse of time can be improved, and additionally a high displacement can be showed with a good reproducibility by suppressing a phenomenon such as drifting or the like, as a displacement as a device with lapse of time, to extremely small levels.
It should be noted that, when fabricating a device of a structure according to the present invention, in addition to all parts integrally sintered, a laminate divided in a mutually opposing direction of thin plate portions, namely a ceramic laminate composed of one thin plate portion and members constituting in the future a fixing portion and a movable portion in rectangular solid forms is prepared, a piezoelectric/electrostrictive element is formed by the screen printing so that the element overlaps a thin plate portion and a movable portion and/or a fixing portion of the ceramic laminate, and at least two sintered structures each formed by integrally sintering with the ceramic laminates are prepared, and by bonding the sintered structures so that the thin plate portions are separated away from each other, namely by bonding each of the above-described portions to be the fixing portion and the movable portion in the future so as to combine by using an adhesive or the like, thus a device can also be obtained. However, since a device fabricated by integrally sintering all members does not have, in a structure, a discontinuous portion like a bonded portion where a third member intervenes, the device is superior in stability and reliability even if a stress is applied to the device by operation of the driving portion, thus it is desirous to form a device by a method of integrally sintering all members as described above without using an adhesive or the like.
Further, it is preferable that, in a piezoelectric/electrostrictive device according to the present invention, a piezoelectric/electrostrictive film constituting a piezoelectric/electrostrictive element is composed of a material including lead zirconate, lead titanate, and lead magnesium niobate as a major component, and a material composed of sodium bismuth titanate as a major component is also preferable. As will be appreciated, details of materials to be used are hereinafter described.
Furthermore, according to the present invention, an optical shutter is provided. The optical shutter is for controlling transmission and shielding of light by relatively moving two shields, and at least one of the shields is mounted on a movable portion of the above-described piezoelectric/electrostrictive device.